1. Field of the invention
The present invention relates to a battery charging apparatus. More specifically, the present invention relates to a full-charge detecting apparatus which detects a fully charged state of a chargeable battery such as a Ni-Cd battery when such a battery is rapidly charged.
2. Description of the prior art
One example of a full-charge detecting apparatus provided in a battery charging apparatus so as to detect that a battery is fully charged is disclosed in, for example, Japanese Patent Publication No. 18177/1985 published on May 9, 1985, and U.S. Pat. No. 4,792,743 issued on Dec. 20, 1988.
In either one of the above described prior arts, a full-charge is detected by utilizing a characteristic of a terminal voltage of a battery being charged. More specifically, in accordance with such a characteristic of the terminal voltage of the battery being charged, as shown in FIG. 5, a peak point A of the terminal voltage appears shortly before the battery enters a fully charged state and the terminal voltage gradually decreases after the peak point A. Therefore, when the terminal voltage becomes lower than the terminal voltage at the peak point A by a predetermined value (.DELTA.V) or more, it is detected that the battery enters a fully charged state.
In either one of the above described prior arts, no measures are taken to deal with a case where a terminal voltage of a battery being charged abnormally varies due to a noise or the like. Therefore, in the prior arts, in a case where the terminal voltage is temporarily raised due to a noise as shown by a difference character B in FIG. 6, the voltage which is raised by the noise is erroneously held as a terminal voltage at a peak point, and consequently, a full-charge may, in some cases, be detected before the terminal voltage actually enters a fully charged state. In addition, in a case where a contact resistance between a charger and a battery is increased due to vibration or the like during a charge and thus the terminal voltage is temporarily decreased as shown by a reference character C in FIG. 7, since it is determined that the terminal voltage decreases more than the predetermined value (.DELTA.V), a full-charge may, in some cases, be erroneously detected.